As the Denver Broncos barrel into the most important offseason in years, there’s an optimism among the team’s fan base that adding a top quarterback would be enough to bring the Broncos back to contender status, instead of the playoff also-rans they’ve been since winning Super Bowl 50.

To believe that, however, is to ignore the very nature of today’s NFL; on ongoing cyclone of activity in which the top teams are raided of their talent and bottom-feeders can improve quickly with shrewd maneuvering. After swinging and missing on Paxton Lynch, the Broncos do indeed need a quarterback — desperately — but a look at the Broncos’ 2015 and 2017 rosters illustrate how different the team looks after only two short years.

2015 2017
QB1 Peyton Manning Trevor Siemian
QB2 Brock Osweiler Brock Osweiler

At quarterback, there’s no comparison. Even in Manning’s final season, when his arm strength all but evaporated, he still knew more about NFL football and could read defenses better than all of the 2017 Broncos’ quarterbacks — combined. Denver may have to spend $30 million or more per season to secure Kirk Cousins’ services just to fill the vacuum left by Manning’s retirement.

2015 2017
RB1 Ronnie Hillman C.J. Anderson
RB2 C.J. Anderson Devontae Booker
RB3 Juwan Thompson Jamaal Charles

One could make the argument that the Broncos’ running game was slightly improved in 2017, thanks to C.J. Anderson’s 1,007-yard season, but it wasn’t as dynamic on the whole. In 2015, Ronnie Hillman and Anderson combined for 1,583 yards on the ground. The 2017 Broncos duo of Anderson and Devontae Booker combined for only 1,306, and free-agent addition Jamaal Charles was curiously relegated to an afterthought.

2015 2017
WR1 Demaryius Thomas Demaryius Thomas
WR2 Emmanuel Sanders Emmanuel Sanders
WR3 Jordan Norwood Bennie Fowler
WR4 Bennie Fowler Cody Latimer

The dynamic duo of Demaryius Thomas and Emmanuel Sanders provide one of the main reasons to believe that the current Broncos’ roster isn’t far removed from their Super Bowl-winning version, but while both receivers had 1,000-yard seasons in 2015, Thomas was the only Broncos’ receiver to finish with more than 555 yards in 2017 and finished with a disappointing 949. In both seasons, no other receiver besides Thomas and Sanders had a significant presence in the offense.

2015 2017
TE1 Owen Daniels Virgil Green
TE2 Vernon Davis A.J. Derby

One of the most glaring drop-offs over the last two seasons has been tight end play. Owen Daniels and Vernon Davis combined for 690 yards in 2015; Virgil Green and A.J. Derby combined for 415. 224 of those came from Derby, who was released mid-season and still finished as the Broncos’ top receiving option at the position. The Broncos desperately hope that former Michigan standout Jake But can make a full recovery from ACL surgery and claim the starting role in 2018.

2015 2017
LT Ryan Harris Garret Bolles
LG Evan Mathis Max Garcia
C Matt Paradis Matt Paradis
RG Louis Vasquez Ronald Leary
RT Michael Schofield Menelik Watson

The Broncos’ dirty little secret in the Manning era? Their offensive line wasn’t all that good, instead counting on Manning’s ability to recognize blitzes and coverages — and then selecting the perfect audible to compensate. That said, even though rookie left tackle Garret Bolles showed real promise in 2017, there wasn’t a single player on the line that outplayed their 2015 counterpart… and that includes even Michael Schofield, who was abysmal during his time with the Broncos, but at least failed at it more cheaply than free-agent addition Menelik Watson.

2015 2017
DE1 Malik Jackson Derek Wolfe
DE2 Derek Wolfe Adam Gotsis
NT1 Sylvester Williams Domata Peko
DL4 Vance Walker Shelby Harris

Malik Jackson left as a free agent after Super Bowl 50 to spearhead a Jacksonville defense that, in 2017, looked like the NFL’s best. The Broncos’ 2017 version notably featured the ageless Domata Peko, who might have been the heart of the defense last season, and Raiders castoff Shelby Harris, who looked like a late-blooming steal. The 2017 Broncos’ line wasn’t as good as the 2015 version thanks to Jackson alone, but Peko and Harris have been huge improvements over former first-round pick Sylvester Williams.

2015 2017
OLB1 Von Miller Von Miller
OLB2 DeMarcus Ware Shaquil Barrett
ILB1 Brandon Marshall Brandon Marshall
ILB2 Danny Trevathan Todd Davis
LB5 Shaquil Barrett Shane Ray

At linebacker, Von Miller remains the standard-bearer; a game-breaking terror for opposing passers who’s every bit as good two years later. In the middle, Brandon Marshall remains a steadying force and Shaquil Barrett (a restricted free agent to-be this spring) is on the rise. That said, he hasn’t reached the lofty status that DeMarcus Ware held, and Danny Trevathan’s sideline-to-sideline speed made him a more explosive player than Todd Davis. While the 2015 unit was marginally better, Denver’s linebacking corps has remained one of the Broncos’ greatest strengths.

2015 2017
CB1 Aqib Talib Aqib Talib
CB2 Chris Harris, Jr. Chris Harris, Jr.
CB3 Kayvon Webster Bradley Roby
S1 T.J. Ward Darian Stewart
S2 Darian Stewart Justin Simmons
S3 David Bruton Will Parks

In 2017, the “No-Fly Zone” met its end when safety T.J. Ward was released prior to the season. While the sky’s the limit for youngster Justin Simmons, Ward’s presence and reputation as one of the league’s hardest hitters proved impossible to reproduce. Bradley Roby is an improvement over the underrated Kayvon Webster, but David Bruton’s versatility is still missed. Despite their losses over the last two years, the Broncos’ backfield is the strongest part of the team… but in 2018, both Aqib Talib and Darian Stewart might be playing somewhere else as the Ward playbook may find itself opened once more. If that happens, the drop-off will be sizable, and this group will likely go from elite to merely above-average.

2015 2017
K Brandon McManus Brandon McManus
P Britton Colquitt Riley Dixon
KR Omar Bolden Isaiah McKenzie
PR Emmanuel Sanders Devontae Booker

The Broncos’ special teams unit was an abject disaster for much of the season. Kicker Brandon McManus finished strong and punter Riley Dixon has effectively replaced Briton Colquitt, but Denver’s return game may have caused more harm then good last season and desperately needs an overhaul. In a league where one-score games are the norm, the Broncos’ regression here has been especially damaging.

Would adding an established free-agent quarterback like Cousins make a huge difference in the Broncos’ likely fortunes in 2018? Of course… but the Broncos are still further away from that championship squad than it initially appears. While the linebacking corps and defensive backfield come close, the truth is that there isn’t a single unit on the 2017 Broncos team that was better than its 2015 iteration — something to keep in mind as the Broncos’ braintrust tries to re-establish itself as a Super Bowl contender once more.

After successive seasons missing the playoffs, there’s no question that Denver’s rebuild starts at the quarterback position — but if the Broncos end there, it’s entirely possible that streak will extend into its third season.

There’s much work left to be done, and the first step is recognizing how much is truly in front of them.